Conventional devices for driving screws using a power tool, such as an electric drill or an impact driver, are well known in the art. Such devices have a driveshaft end that is attached to the drive mechanism of the power tool and a screw driving head with a screw bit tip that engages the head of a screw. Screw driving heads now include devices with drive mechanisms that allow a screw to be countersunk at or below the surface of a work piece. For example, a clutch system may disengage the driveshaft to stop the bit from turning when a predetermined countersink depth is achieved. At the predetermined countersink depth, rotation of the screw bit ceases and the driving of the screw stops.
One disadvantage with most prior screw driving heads is that the countersink depth is fixed, or may be adjusted only by changing the screw bit because the countersink depth is determined by the length of the screw bit itself. As understood by those skilled in the art, screw bits are generally not available in small length increments, so countersink depth adjustment in such devices is impractical. Consequently, screw driving devices with depth adjustment have been invented.
One such screw driving device is adjusted by performing a series of steps. First, an outer collar is unscrewed from a nozzle. Next, both the outer collar and nozzle are moved axially by rotating each separately to achieve a desired counter sink depth. Finally, the outer collar is tightened down on the nozzle to lock the screw driving device at the desired counter sink depth. Manufacturers of such tools include Black & Decker, DeWalt, Roby, Milwaukee, etc.
Another such adjustable screw driving device is described in U.S. Pat. No. 4,647,260, which teaches a depth-adjusting subassembly connected to a nose portion of a power tool. An incremental rotation of a depth-adjustment collar of the depth-adjusting subassembly form one angular position to another relative to a nose portion of the power tool produces an axial movement of a dept locator to adjust a depth setting of the depth-adjusting subassembly. While simple to adjust, the depth-adjusting subassembly requires a plurality of precision parts.
It is therefore an object of the invention to provide a screwing device with an adjustable countersink depth that is simple to construct and to operate.